A variety of metabolic substrates will be added to the perfusates of isolated blood perfused dog kidneys in an attempt to improve the urinary acidification process in this preparation. Hemodynamic studies in isolated perfused kidneys will focus on mechanisms of angiotensin tachyphylaxis and reversal, and the relationship of plasma oncotic pressure to autoregulation of renal blood flow. Marked elevations of plasma oncotic pressure will be produced to diminish the glomerular filtration rate and enhance tubular reabsorption of water in an effort to produce a model of acute renal failure in isolated kindeys which may have relevance to clinical forms of this entity.